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Show 970 ON CRUSTACEANS OF THE GENUS SERGESTES. [Dec. 1, common at the surface, but Ortmann communicates that it has been captured in the intermediate net from 700-500 m.; and if some of the specimens recorded by Bate (p. 390) as 38, 43, and 50 m m . long, and coming respectively from 600, 2150, and 345 fathoms, really belong to this species, it grows considerably larger in the deep" sea, as no specimen from the surface exceeds 30 m m . Finally, S. cornutus, Kr., and 8. edwardsl, Kr., are the only instances of the 14 species which only have been captured at the surface (and in vertical nets drawn up from 500 m. to tbe surface). In this paper I. have described the mature forms of S. vlgilax, Stimps., H. J. H., S. penerlnkl, Bate, H . J. H., and S. Incertus, n. sp., which have all been captured at the surface. S. tenulremls, Kr., H. J. H., and S. corniculum, Kr., H . J. H., are common at the surface in the Mastlgopus-stages ; above I have described the younger black-eyed forms of both species, also captured at the surface, but the adult stages are quite unknown and must, in my opinion, be true deep-sea forms. Of 8. dlapontlus, Bate, and S. mediterraneus, m., only the Mastlgo pus-forms are known, and the adults are certainly inhabitants of the depths. (S. profundus, Bate, from 1375 and 2550 fathoms, I omit, as the species is too uncertain.) Though we still know too little of the bathymetrical distribution, it must, I think, be taken as proved that at least two-thirds of the species Inhabit the depths of the sea when the animals have quite arrived at maturltg (or at least at their full length, cfr. S. atlanticus). I can say that with two exceptions-my single adult specimen of 8. Incertus, m., and Kroyer's specimen of S. arcticus, Kr.,-no specimen exceeding 30 m m . iu length recorded in the existing literature or seen by m e has been captured near the surface, but all large specimens, from 30 m m . to 113 m m . (S. Inous, Fax.) in length, have been secured with trawl or dredge coming from a considerable to a very great depth (345-2574 fath.). Faxon writes on p. 249 : " There can be no doubt that the deep-sea Crustacea occasionally come to, or very near to, the surface," and he communicates several instances; I think that, for instance, m y single and large specimen of S. Incertus, m., 47 ram. long, has been secured on such a visit. It is evident that tbe animals as true swimming forms do not live on the bottom itself, but, I presume, in tbe water-stratum just above it. As will be seen from this paper, our knowledge of this rich and curious genus is still rather imperfect. A good monograph, based on the study of the collections in the seven or eight museums which possess materials of importance, would be extremely valuable and elicit numerous new facts; and future deep-sea expeditions, making use of the trawl, intermediate net, vertical net, and surface net, would be sure to discover new species and especially enlarge our knowledge of the metamorphosis and distribution. |
